1. Field of Invention
The present invention relates to thermometers and more particularly to an electronic thermometer and temperature prediction method therefor in which a compensation coefficient is included in the predictive mode and a symmetrically shaped probe is employed so as to rapidly precisely obtain a stabilized temperature measurement.
2. Related Art
Conventionally, there are two kinds of probe, i.e., contact based thermometer such as glass bulb thermometer incorporating a heat responsive mercury column. Such glass bulb thermometer is disadvantageous in that it usually takes 2 to 8 minutes to reach a thermal equilibrium between thermometer and a patient""s body temperature prior to taking the patient""s temperature. Further, the calibrated temperature scale of glass bulb thermometer is not easy to read and thus, measurements are prone to human error.
Another kind of thermometer is non contact based thermometer such as an electronic thermometer. The provision of electronic thermometer aims at minimizing or eliminating these disadvantages. A typical electronic thermometer comprises a probe for sensing the temperature of a selected part of human body, a processor for processing temperature data, and a display for displaying temperature values.
For rapidly obtaining an accurate temperature, a temperature sensitive electronic probe coupled with prediction circuitry is provided in the electronic thermometer so as to obtain a direct display of the patient""s temperature before the probe has reached equilibrium with the patient. With this approach, assuming the patient""s temperature is not significantly changing during the measurement time. Typically, prediction of temperature is performed by monitoring the measured temperature over a period of time and the rate of change thereof. and processing these two variables to predict the patient""s temperature. The advantage of this predictive thermometer is that a rapid temperature determination offers more timely diagnostic information. However, a disadvantage with such a thermometer is that the accuracy with which temperature is predicted declines markedly unless the processing and analysis of the data are accurately performed.
The accuracy of predicted temperature is strongly depended on the predictive mode employed in the stabilized temperature prediction method. For example, a temperature prediction equation is programmed to estimate a temperature rise curve in a conventional electronic predictive thermometer. This prediction equation obtains an increment from sampled temperature points. This increment is added to actually measured temperature. As such, a predicted stabilization temperature is obtained prior to reaching an equilibrium between thermometer and the patient. For achieving this, some parameters are predetermined for decreasing errors in the equation. It is known that temperature rise curves of different persons are different. Even the temperature rise curve of mouth is different from that of armpit in the same person. As such, the prediction equation even in conjunction with temperature characteristics of probe used in estimating the stabilized temperature, an accurate prediction of temperature is still not possible.
One prior art approach is disclosed in U.S. Pat. No. 5,738,441 in which the processor selects the first time frame from a time period occurring before the sensor reaches the temperature of the object and uses the logarithm of the characteristics of the temperature signals of the first time frame to calculate a prediction of the temperature of the object. This approach may rapidly predict the temperature of object based on the assumption that the object has an unlimited heat source. However, the heat source of human body is limited. Thus this assumption is not supported, thereby limiting the application of this patent. Another limitation not considered in the patent is the characteristics of probe. It is understood that sensor incorporated in probe is critical to the accuracy of temperature prediction. In detail, probe must uniformly transfer heat to sensor for obtaining an accurate value. However, factors such as dissipation in the heat transfer process, location of sensor, and so on all affect the accuracy of temperature prediction.
Another U.S. Pat. No. 5,632,555 discloses an electronic thermometer for decreasing the heat dissipation. This approach preheats sensor to predict temperature of the object, thereby eliminating errors caused by various factors during predicting process. This temperature prediction approach is rapid as well as significantly decreases errors. But this is unsatisfactory for the purpose for which the invention is concerned for the following reasons:
1. Additional electronics and power are required to effect a preheating.
2. Not cost effective. Thus the relatively high manufacturing cost inhibits its commercial availability.
It is thus an object of the present invention to provide an electronic thermometer and temperature prediction method therefor in which a compensation coefficient is included in the second-order predictive mode for eliminating errors caused by various factors during predicting process so as to rapidly precisely obtain a stabilized temperature measurement.
It is another object of the present invention to provide a temperature prediction method which only involved simple calculation and adjustment, thereby decreasing the time required to predict the stabilized temperature.
It is still another object of the present invention to provide an electronic thermometer for effectively decreasing error during the heat transfer process by providing a symmetrically shaped probe.
The advantages of the present invention are realized by providing an electronic thermometer and temperature prediction method therefor. The thermometer comprises a sensor and a processor wherein the sensor is provided in a symmetrical point in a symmetrically shaped probe for sensing the temperature data of a selected part of body and outputting the time dependent temperature data; and the processor functions as receiving output temperature data and combining the temperature data with a compensation coefficient to obtain a compensated temperature data. This effects to obtain an accurate prediction temperature before the probe reaching equilibrium with the body. The equation describing this process is as below:                               y          2                =                              y            1                    +                      α            ⁢                          xe2x80x83                        ⁢                                          ⅆ                                  y                  1                                                            ⅆ                t                                                                        (        A        )            
where xcex1 is the compensation coefficient which is obtained empirically from a person""s mouth, armpit, or anus, y1 is sensed temperature, and y2 is electronic thermometer temperature data.                     B        =                              y            2                    +                      τ            ⁢                          xe2x80x83                        ⁢                                          ⅆ                                  y                  2                                                            ⅆ                t                                                                        (        B        )            
B is the temperature of measured object, xcfx84 is characteristics constant.
By substituting equation (A) into equation (B), an expanded equation is obtained:   B  =            y      1        +                  (                  α          +          τ                )            ⁢              xe2x80x83            ⁢                        ⅆ                      y            1                                    ⅆ          t                      +          α      ⁢              xe2x80x83            ⁢      τ      ⁢              xe2x80x83            ⁢                                    ⅆ            2                    ⁢                      y            1                                    ⅆ                      t            2                              
where y, and compensation coefficient xcex1 are known. Thus a stabilization temperature is obtained by applying sensed temperature into the above second-order differential equation for processor to process.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.